Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $217.29   11.671%   $242.6499   $242.65   $242.65   $242.60  
  Purchase #2 $50.56   11.358%   $56.3026   $56.30   $56.30   $56.30  
  Purchase #3 $231.51   11.274%   $257.6104   $257.61   $257.60   $257.60  
  Purchase #4 $245.97   5.318%   $259.0507   $259.05   $259.05   $259.10  
  Purchase #5 $29.70   13.201%   $33.6207   $33.62   $33.60   $33.60  
  Purchase #6 $153.98   7.486%   $165.5069   $165.51   $165.50   $165.50  
  Purchase #7 $208.93   9.269%   $228.2957   $228.30   $228.30   $228.30  
  7 purchase totals = $1,137.94       $1,243.0369   $1,243.04   $1,243.00   $1,243.00